We told their military that if they didn't surrender, we would start bombing them again, with new weapons.
We dropped one nuke, and the Japanese military didn't surrender then.
It took two of the most horrific and destructive weapons in history to make them surrender.
If you're going to blame someone for ruining so many people's lives, blame the fanaticism of the Japanese Military of that time for refusing to surrender, and for teaching their people to fight and die, even if there's no way to win.
You also need to think of all the US and Japanese soldiers that would have died if a mainland invasion took place.
You're also a naive idiot if you think the winners in War don't commit atrocities, as well.